Question

Sodium hydroxide or caustic soda is a useful industrial chemical and is manufactured by chlor-alkali process. In the process, a gas X is formed as the by-product. It reacts with slaked lime to give a compound Y which finds application as a bleaching agent for the clothes. Name the gas X and the compound Y formed?

Answer 1

Chlor-alkali process:

In this process, electricity is passed through sodium chloride$\left(\mathrm{NaCl}\right)$ which decomposes to form sodium hydroxide $\left(\mathrm{NaOH}\right)$, hydrogen $\left({\mathrm{H}}_2\right)$ and chlorine $\left({\mathrm{Cl}}_2\right)$ as a by-product.

Reaction involves:

$2\mathrm{Nacl}\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\stackrel{\mathrm{Electrolysis}}{\to }2\mathrm{NaOH}\left(\mathrm{aq}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$

Gas X :

The gas X is the by-product of the above process which is Chlorine $\left({\mathrm{Cl}}_2\right)$.

Now this chlorine reacts with slaked lime $\left(\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\right)$ to form compound Y.

Compound Y:

Reaction involves:

$2\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)+2{\mathrm{Cl}}_2\left(\mathrm{g}\right)\stackrel{}{\to }\underset{\mathrm{Bleaching}\mathrm{Powder}}{\mathrm{Ca}{\left(\mathrm{OCl}\right)}_2\left(\mathrm{s}\right)}+{\mathrm{CaCl}}_2\left(\mathrm{s}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

The product formed from the above reaction is compound Y which is Calcium oxychloride $\left({\mathrm{CaOCl}}_2\right)$.

It is used as a bleaching agent for clothes.

Thus, the gas X is Chlorine $\left({\mathrm{Cl}}_2\right)$ and the compound Y is Calcium oxychloride $\left({\mathrm{CaOCl}}_2\right)$.